1. Field of the Invention
This invention relates to an expandable reaming tool which can be used to drill out and ream well bores and more particularly relates to a reamer having expandable blades suitable for use in oil and gas drilling and method.
2. History of the Prior Art
When drilling a well bore, typically a large hole is first created into which is inserted a length of casing which lines the bore hole. The casing may be cemented in place and serves to prevent the bore wall from collapsing. In order to drill deeper into the bore a smaller drill bit is used together with a narrower casing to slide through the previously installed casing. Consequently, each progressive section of the bore, and the casing installed within it, has a smaller diameter to that which is above it.
When it is desired to drill a hole below an upper casing of a diameter larger than the bore of such upper casing, an expandable reaming tool is used. Such tools, sometimes referred to as underreamers, comprise a body having one or more expandable arms/blades which can move between a closed position, when the underreamer is of a narrow diameter, to fit through such upper casing, and an open position, when such underreamer expands to bore a hole below such upper casing of larger diameter than its body.
A typical prior art expanding reamer tool is shown in FIGS. 1(a) and (b). Tool 10 comprises a body 12, reaming blades 14 and 16 pivotally mounted thereon and a cam 18 to actuate reaming blades 14 and 16 from a closed position, shown in FIG. 1(a), for insertion through a well bore or narrow diameter upper casing, to an open position, shown in FIG. 1(b), for boring a wider diameter bore hole.
Such prior art reaming tool has a number of disadvantages. First, cam members 20 and 22 which are mounted on the periphery of the top of cam 18 are prone to key seating on the lower surfaces of outer mounting arms 24 and 26 of reaming blades 14 and 16 due to the constant pressure exerted on cam members 20 and 22 during boring. Secondly, the closing diameter of the tool is limited by the wide separation of cam members 20 and 22 as the cam ratio decreases by approximately three to one when reaming blades 14 and 16 open. Further, the proximity of cam members 20 and 22 to the outer edge of body 12 also leads to their being damaged by collisions with irregularities on the bore wall.
It is therefore an object of at least one embodiment of the present invention to provide a reaming tool which overcomes the aforementioned disadvantages or the prior art and provides increased stability while boring compared to the prior art.
Therefore in a first aspect of the present invention there is provided an expandable reaming tool with the tool comprising a body having a central support member along its central axis, first and second reaming blades pivoting on a spindle mounted perpendicular to the central axis, and means for laterally extending the blades from a closed position to an open position, wherein on the spindle is arranged in order: an outer mounting arm of the first reaming blade, and an inner mounting arm of the second reaming blade, the central support member, an inner mounting arm of the first reaming blade, an outer mounting arm of the second reaming blade; and the means for laterally extending the blades being at least one cam disposed immediately adjacent to said central support member, said cam actuable on at least one of the inner mounting arms of the reaming blades.
In a preferred embodiment the central support member includes a central reaming portion. The central reaming portion can be located on the end of the central support member and can be arranged as a spade point. Advantageously the central reaming portion can be located adjacent to the blades such that it is covered by the blades when the blades are in the closed position.
The blades can be mounted on a leading end of the tool. Each blade can have an outer surface, such outer surfaces being substantially plano-cylindrical such that when the blades are in the closed position they present a substantially cylindrical body with a diameter equal to the diameter of the drill body.
The blades can each include front and inner reaming portions. The front reaming portion can be located on the leading end of each of the blades when the blades are in the closed position, and the inner reaming portions can be located on the inner plano surface as seen when the blades are in the open position. Additionally the blades can include outer reaming portions on the cylindrical outer surface. The blades can further include a stop. The stop is used to restrict the lateral extension to a maximum projection. Preferably the stop is located on a lower of each blade surface between the mounting arms. The cam is slideably mounted on the central support member. An inner aperture of the cam mates closely with the outer surface of the central support member. In this way the cam can more smoothly along the central axis supported by the central support member.
The cam can, in a preferred embodiment, include two cam members. The cam members can be projections from the cam on the leading surface of the cam. The cam members can be arranged to closely abut the central support member. Further the cam members can be dimensioned to fit between the central support member and the outer mounting arms of the blades. The cam members are of a size to project upward from the cam a distance which is shorter than the distance between the leading edge of the cam and a lower surface of the outer mounting arms when the blades are in a closed position. When the cam moves up the central support member, the leading edge of each cam member passes inside the space between the outer mounting arms of each blade and the central support member and only contacts the lower surface of at least one of the inner mounting arms to force the blades into an open position. The cam member do not strike or actuate the outer mounting arms.
Thus the device of this invention provides a method of laterally extending an expandable reaming tool, such method including the steps of driving the cam along the central support member and on its journey, causing contact of the cam members mounted on the cam against the lower surfaces of the inner mounting arms of the blades to force the blades to laterally extend, and as the blades laterally extend causing contact of the lower surfaces of the outer mounting arms against the leading edge of the cam.
Such method can further include the step of stopping the lateral extension of the blades at a desired lateral extension. In a preferred method the blades are stopped when a stop member meets the central support member.
Such preferred method can include stopping the lateral extension of the blades when the blades are at an angle of 75 degrees from the central axis.